A known example of common lighting devices is a lighting device 900 shown in FIG. 62.
The lighting device 900 has a collimating optical system LC which includes a meniscus lens L1 and an aspherical lens L2 and is configured such that a LED light source 10 is placed at the focal position of this optical system as shown in FIG. 62.
Here, light emitted from a point on the optical axis AX of the LED light source 10 is collimated light which is parallel to the optical axis AX as shown in FIG. 62. On the other hand, since the LED light source 10 is a surface light source rather than a point light source, there is light emitted from a location away from the optical axis AX. The light emitted from a location away from the optical axis AX travels in a direction which is different from the optical axis AX and therefore reaches a place which is different from that the light emitted from a point on the optical axis AX reaches. Thus, there is a problem that illuminance uniformity is not achieved across the illuminated surface.
Moreover, since the meniscus lens L1 and the LED light source 10 are distant from each other, there is a probability that light emitted from the LED light source 10 at a large angle is not incident upon the meniscus lens L1.
Patent Documents 1 and 2 disclose light sources which can utilize almost all of light emitted from a LED emitter.
The light source disclosed in Patent Document 1 has a LED emitter, an inner lens enclosing the LED emitter, and a meniscus lens covering these components. The light source disclosed in Patent Document 2 has a LED emitter and a meniscus lens covering the LED emitter with a gap provided therebetween. In these light sources, a virtual image Vl1 formed by an inner surface of the meniscus lens is produced at a position outer than the LED emitter (on the light exit surface side of the lens).
As described above, when the virtual image Vl1 formed by the inner surface of the meniscus lens is produced at a position outer than the LED emitter, almost all of light emitted from the LED emitter is incident upon the meniscus lens. This improves the light utilization efficiency of the light emitted from the LED emitter.